(1) Field of the Invention
The present invention relates to a developing unit for use in an image forming apparatus such as a laser printer, copier, facsimile machine etc., in order to replenish the developer for image development to the developing vessel as a part of the developing unit and in particular relates to a structure of a developer cartridge for replenishing the developing unit with the developer when it is used up.
(2) Description of the Prior Art
An image forming apparatus such as a laser printer, copier, facsimile machine, etc., utilizing the electrophotographic technique, has an image forming portion for forming a desired image on a sheet for recording. In this image forming portion, the surface of a photoreceptor as an image bearer is uniformly electrified with charge of a particular polarity and then is illuminated with an optical image so as to form a static latent image corresponding to the image. For the purpose of visualizing this static latent image, the image forming portion includes a developing unit and other components. The developing unit is configured of a developing vessel holding a developer and having a developing roller etc., for supplying the developer to the developing position where the developing roller opposes the photoreceptor. Further, since the developer in the developing vessel is consumed, a toner replenishing device for supplying the developer, or for instance, a toner, to the developing vessel as necessary is arranged adjacent to the developing vessel. When the toner in this toner replenishing device is used up, a developer cartridge is set for replenishing so that the toner contained in the cartridge is supplied.
The above developer cartridge is configured of a container box having one side open and containing the developer therein with its opening attached with a removable sealing member so as to package the developer in the container box. In this configuration, a door provided for the opening for replenishment of the toner replenishing device is opened and then the developer cartridge is fitted to the opening so that the sealing member opposes the opening of the door. In this position, when the sealing member is removed, the stored developer is supplied the toner replenishing device through the opening.
According to the developer cartridge having the above configuration, when a cartridge body 100 in FIG. 1 is set to the opening of a developer storage hopper 101 of the toner replenishing device as shown in FIG. 1 and a sealing member 102 is stripped from the cartridge body 100 side, developer (toner) T inside cartridge 100 falls into hopper 101. At this moment, toner T fills hopper 101 sequentially in the order of unsealing of the opening as sealing member 102 is peeled off.
Resultantly, the replenishing of toner T at the area from which sealing member 102 is peeled first differs from the replenishing of the toner at the area where the sealing member is last removed. More illustratively, due to the fluidity of toner T, a large amount of toner T, as indicated by region E1, falls and is supplied to the hopper at the stripping start area of sealing member 102. On the contrary, at the stripping end area of sealing member 102 , a smaller amount of toner is supplied as indicated by region E2.
With this replenished state, if toner T being supplied in hopper 101 is conveyed to the developing vessel, a greater amount of toner is fed at the region where a large amount of toner is replenished in hopper 101 while the replenishing amount of the toner will inevitably be lowered at the stripping end of sealing member 102. To deal with this, an agitator 103 or the like is arranged in order to avoid uneven distribution of the toner being provided to hopper 101, toner aggregation and other defects so as to uniformly distribute toner T after replenishment. However, it is not possible to make the distribution of the toner in the longitudinal direction uniform immediately, so stable replenishment of the toner to the developing vessel cannot be expected before this is completed.
Resultantly, it is impossible to carry out development of uniform density because of imbalance of the distribution of the toner amount in the developing unit, and hence this may cause image defects.
To deal with this, Japanese Utility Model Application Laid-Open Hei 6 No.33158 discloses a configuration as shown in FIG. 2, in which partitions 104 are provided to divide the body of a developer cartridge 100 into sections of the same width, wherein each section, separated by partitions 104, is filled up with the same amount of toner T. This configuration eliminates variations in the supplied amount of toner at the edge area as shown in FIG. 1.
However, it is necessary to provide each partitioned section with the same amount of toner when it is manufactured, so this configuration needs a careful packaging operation. Further, since partitions 104 for partitioning the body of cartridge 100 are needed, resulting in high manufacturing cost for cartridge 100 body.
There is another configuration, which is disclosed in Japanese Patent Application Laid-Open Hei 10 No.104923 in which a vibrating member is provided on the developer storage hopper 100 side so that the vibrating member is activated during replenishing to thereby make the developer that fills developer storage hopper 100 uniform. This configuration is advantageous in that the supplied developer can be uniformly leveled off, but needs a vibrating member and a circuit for driving the vibrating member in linkage with the replenishing operation of the developer, leading to a rise in cost.
On the other hand, Japanese Patent Application Laid-Open Hei 3 No.71166 discloses a developer cartridge 100 of which the shape of the container box is manipulated so the toner can be supplied in a greater amount on the side from which the sealing member starts to be stripped and the charged amount of toner is continuously decreased in the stripping direction, as in FIG. 1. With a developer cartridge having such a shape, a further greater amount of the developer will be supplied at the stripping start area while a markedly lowered amount of developer will be supplied at the stripping end area, as is apparent from the consideration of the toner's fluidity. As a result, when the developer is replenished to the developing vessel having a developing roller, the replenished amount of the developer becomes extremely large at one end and extremely small at the other end with respect to the direction of the rotary axis of the developing roller.
This causes a marked imbalance in the amount of the developer replenished to the developer vessel, which leads to variations in developing density, etc. along the direction of the rotary axis, only resulting in markedly awkward development.